This invention relates to a turbojet engine having at least one axially movably arranged sliding valve to optionally shutoff or expose the engine by means of surface sections which are vaulted with respect to the valve centerline and are mated to a stationary companion surface on an annular casing lip.
In the state of the art axially movable or adjustable, drop-shaped or mushroom-shaped sliding valves in the form of predominantly self-enclosed bodies are generally provided as shutoff or control means on gas turbine or turbojet engines. With such sliding valve designs in, e.g., drop or mushroom shape and with an axis symmetrically divergent/convergent contour in the direction of flow, a circular cylindrical shutoff face is formed at the point of maximum valve diameter. This construction results in comparatively large valve diameters that are out of reasonable proportions compared with the engine or component diameters being achieved today which despite high engine performance and mission envelopes, give or should give comparatively low frontal area drag. A shutoff valve of said type to be arranged at, e.g., the inlet end accordingly requires, in view of achievable performance and thrust goals, a relatively large minimum overall diameter despite a comparatively small engine diameter to safely provide in its open position a relatively large mass flow in keeping with the requisite Mach numbers of the flow.
Such sliding valve concepts, again, provide an advantage in their comparatively great component strength while using only a small variety of parts and posing little risk of trouble for the entire shutoff system, especially to multiple-flap exit nozzle type concepts and the like. The risk of fragment ingestion and damage to the engine is here very low indeed.
Such sliding valve concepts can be employed, e.g.:
to shutoff or expose a "normal" turbojet engine, e.g., a straight-flow engine, at the air inlet end and/or the gas outlet end from or to the environment in an aerodynamically clean configuration; this conceivably involves an aircraft concept exhibiting separately arranged ramjet and turbojet engines, the latter to be shutoff and immobilized in straight ramjet operation;
to permit splitting, e.g., a mass flow (fan) optionally over an inner and/or outer engine flow path in the case of a double-flow or bypass turbojet of variable power distribution (changeover engine);
to shut off the respective basic turbine engine in the straight ramjet mode of a compound turbojet-ramjet engine from the ram-air flow at the air inlet end and the gas flow at the exit end, respectively; assuming, e.g., a ram-air duct of annular construction which envelopes the basic turbine engine and which at its front end has a common variable air inlet (ground start to hypersonic flight operation) for the basic engine and the ramjet portion of the engine; where downstream of the hot gas exit (nozzle) of the basic engine the ram-air duct can issue into a portion containing afterburning and additional burning (ramjet propulsion) features plus the adjoining variable exit nozzle. In connection with said last mentioned compound engine concept a variant might conceivably be used with a front fan which is immobilized in the ramjet mode and which in subsonic operation delivers into the ram-air duct which then serves as a bypass duct for the secondary flow.
In a broad aspect, an object of the present invention is to provide a suitable engine shutoff valve concept for said potential applications which in design and relative arrangement with the turbojet or basic turbine engine provides an aerodynamically clean (environment) slim overall engine at simultaneously clean configuration for optimum shutoff or opening at the air inlet end and/or the hot gas end.
This object is achieved according to the present invention by providing an arrangement, wherein the valve has vaulted surface sections which are spaced axially apart and circumferentially angularly offset by essentially 180.degree. relative to the valve centerline and which form its maximum relative diameter.
By using three-dimensionally displaced drop- or mushroom-shaped configuration of the sliding valve in preferred embodiments it is possible to make a straight-flow turbojet engine, e.g., relatively slender or give it a relatively moderate diameter and to provide, in the open position of the valve when the mass flow through the engine is comparatively large (comparatively large thrust requirement), a correspondingly large air inlet flow area into the compressor to suit the specified flow criteria (Mach numbers, etc.). This applies similarly also to a compound gas turbine-ramjet engine, where for subsonic flight operation the basic turbine engine (inside) can be supplied with the requisite amount of intake air through, e.g., an outer annular ram-air duct at the inlet end, in which the relatively slender or small-diameter basic engine makes for an overall engine of relatively low frontal area drag. It is in especially the latter case that the relative increase in overall length of the shutoff valve caused by the invention plays no significant part, for the reason that there is sufficient installation space available for the purpose via the front-end variable air intake of the overall engine.
In oblique cylindrical sectional view of the circular cylindrical casing of the jet engine or basic turbine engine there results, e.g., a moderately uniformly elliptically contoured casing lip against which the shutoff valve with the mating contour of its elliptical circumferential or circular shutoff surface can be moved to shut off the engine at, e.g., the air intake end. It would also be readily feasible, however, to give the engine casing a moderately elliptical shape at least at the end terminating in the direction of the casing lip such that in oblique sectional view of the casing an annular lip with corresponding extreme edge is formed to which the oblique circumferential shutoff surface of the valve would have to be mated cylindrically.
The centerbody (stationary part of system) cooperating in connection with a shutoff valve and enclosing, e.g., an annular air inlet duct predominantly relative to engine casing surfaces, can be made axisymmetrically divergent in a downstream direction from a wall geometry which at first extends inwards asymmetrically with the engine centerline, to form an accelerating, uniform constriction of the duct carrying the airflow in the direction of the compressor inlet. In this manner the irregularities potentially caused in the airflow by the "asymmetry" of the valve can be homogenized over the overall circumference--before it enters the compressor.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.